Engine valve moving device

ABSTRACT

In an engine valve train device in which a crankshaft sprocket  25   b  provided on a crankshaft  8  and an intermediate sprocket  38   a  disposed in the vicinity of camshafts  36, 37  are connected by means of a timing chain  40  and an intermediate gear  38   b  fixed to the intermediate sprocket  38   a  is made to mesh with camshaft gears  41, 42  fixed to the camshafts, the intermediate gear  38   b  is made smaller in diameter than the intermediate sprocket  38   a  and is disposed behind the intermediate sprocket  38 , and furthermore, an inspection hole  38   c ′ is formed in the intermediate sprocket  38   a  for visualizing the meshing portion between the intermediate gear  38   b  and the camshafts gears  41, 42.

TECHNICAL FIELD

The present invention relates to an engine valve train device in which acamshaft is driven to rotate by a crankshaft.

BACKGROUND ART

For example, as valve train devices for motorcycle engines, there existsconventionally a valve train device having a construction in which acrankshaft sprocket provided on a crankshaft and an intermediatesprocket disposed in the vicinity of a camshaft are connected by way ofa timing chain, so that an intermediate gear fixed to the intermediatesprocket meshes with a camshaft gear fixed to the camshaft (for example,refer to JP-A-6-66111).

In the case of the construction in which the intermediate gear fixed tothe intermediate sprocket is brought into mesh engagement with thecamshaft gear, while a construction in which timing or alignment markson the intermediate gear and the camshaft gear are caused to align witheach other is adopted as a construction for carrying out valve timing,since the construction of the intermediate gear requires that theintermediate gear has a smaller diameter than that of the intermediatesprocket, in the event that the intermediate gear is disposed behind theintermediate sprocket, the alignment mark on the intermediate gearbecomes difficult to be observed visually from the outside, and thiscauses a problem that the valve timing work becomes difficult to becarried out when an engine is assembled.

Note that in case a construction is adopted in which an intermediategear is disposed in front of an intermediate sprocket (for example,refer to JP-A-9-250314), while the valve timing work becomes easy to becarried out, a dimension from the camshaft gear to the cam nose, and anarea surrounding the camshaft is enlarged accordingly and the torsionalamount of the camshaft becomes large, leading to a problem that thevalve timing control accuracy is reduced.

The invention was made in view of the problems inherent in theconventional valve train device construction, and a problem that theinvention is to solve is how to provide an engine valve train devicewhich makes the valve timing work easy to be carried out while theintermediate gear is disposed behind the intermediate sprocket and whichcan improve the valve timing control accuracy while avoiding the riskthat the area surrounding the camshaft is enlarged.

DISCLOSURE OF THE INVENTION

According to a first aspect of the invention, there is provided anengine valve train device in which an intermediate driven wheel disposedin the vicinity of a camshaft is driven by a crankshaft-side drivingwheel formed on a crankshaft and a camshaft gear fixed to the camshaftis driven by an intermediate gear fixed to the intermediate drivenwheel, the engine valve train device being characterized in that theintermediate gear is made smaller in diameter than the intermediatedriven wheel and is disposed on a back side of the intermediate drivenwheel, in that an inspection hole is formed in the intermediate drivenwheel for visualizing a meshing portion where the intermediate gear andthe camshaft gear mesh with each other, and in that an alignment mark isformed on a tooth portion of the intermediate gear and the camshaftgear, respectively.

According to a second aspect of the invention, there is provided anengine valve train device as set forth in the first aspect of theinvention, characterized in that the intermediate driven wheel and theintermediate gear are disposed on a crankshaft side across a matingsurface of a cylinder head with a cylinder head cover, whereas thecamshaft gear is disposed on an opposite side to the crankshaft sideacross the mating surface, and in that the meshing portion where theintermediate gear meshes with the camshaft gear is positioned in thevicinity of the mating surface.

According to a third aspect of the invention, there is provided anengine valve train device as set forth in the first or second aspect ofthe invention, characterized in that a position alignment mark whichrefers to the mating surface as a reference surface is formed on anouter surface of the intermediate driven wheel.

According to a fourth aspect of the invention, there is provided anengine valve train device as set forth in the second or third aspect ofthe invention, characterized in that a camshaft carrier is detachablyattached to the cylinder head, and in that the camshaft is rotationallymounted on the camshaft carrier by means of a camshaft cap.

According to a fifth aspect of the invention, there is provided anengine valve train device as set forth in any of the first to fourthaspects of the invention, characterized in that the intermediate drivenwheel is an intermediate sprocket around which a timing chain is woundand is formed integrally with the intermediate gear to constitute anintermediate rotational unit, and in that the intermediate rotationalunit is disposed within a chain compartment formed on a side wall of thecylinder head in such a manner that a rotational shaft of theintermediate rotational unit is located closer to the crankshaft sidethan the mating surface and is rotationally supported via a bearing by asupport shaft which is inserted to be disposed in such a manner as toextend across the chain compartment.

According to a sixth aspect of the invention, there is provided anengine valve train device as set forth in the fifth aspect of theinvention, characterized in that a washer member is disposed between theintermediate rotational unit and a wall surface of the chain compartmentfor regulating an axial position of the intermediate rotational unit andan axial arrangement space for the bearing.

According to a seventh aspect of the invention, there is provided anengine valve train device as set forth in any of the first to sixthaspects of the invention, characterized in that the camshaft gearcomprises a power transmission gear for transmitting a driving forcefrom the intermediate gear to the camshaft and an adjustment gear foradjusting a backlash between the power transmission gear and theintermediate gear, the adjustment gear being made to rotate relative tothe power transmission gear, whereby the backlash is adjusted by causingthe adjustment gear to relatively rotate forward in a rotating directionrelative to the power transmission gear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a right-hand side view of an engine according to an embodimentof the invention.

FIG. 2 is a sectional plan view showing a development of the engine.

FIG. 3 is a left-hand side view showing a valve train device of theengine.

FIG. 4 is a sectional rear elevation of the valve train device.

FIG. 5 is a sectional plan view showing a development of a balance shaftof the engine.

FIG. 6 is a bottom view of a cylinder head of the engine.

FIG. 7 is a bottom view of a cylinder body of the engine.

FIG. 8 is a sectional side view showing a portion where the cylinderhead of the engine is connected to the cylinder body.

FIG. 9 is a sectional side view showing a portion where the cylinderbody of the engine is connected to the crankcase.

FIG. 10 is another sectional side view showing a portion where thecylinder body of the engine is connected to the crankcase.

FIG. 11 is a left-hand side view showing a balancer unit of the engine.

FIG. 12 is an enlarged cross-sectional view of a portion where a holdinglever of the balancer unit is attached.

FIG. 13 is a side view of constituent components of a rotational leverof the balancer unit.

FIG. 14 is a side view showing a damping construction of a balancerdrive gear of the balancer unit.

FIG. 15 is a right-hand side view of the balancer unit.

FIG. 16 is a sectional right-hand side view of a bearing bracket of theengine.

FIG. 17 is a sectional left-hand side view of a bearing bracket.

FIG. 18 is an explanatory drawing showing the construction of alubrication system of the engine.

FIG. 19 is a drawing showing the construction of the lubrication system.

FIG. 20 is a sectional side view of an area surrounding a lubricatingoil pump of the lubrication system.

FIG. 21 is a sectional left-hand side view of the lubrication system.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention will be described withreference to the accompanying drawings.

FIGS. 1 to 21 are drawings for describing an embodiment of theinvention. In the drawings, reference numeral 1 denotes a water-cooled,4-cycle, single cylinder, 5-valve engine, and in general, the engine hasa construction in which a cylinder body 3, a cylinder head 4 and acylinder head cover 5 are stacked on and fastened to a crankcase 2, anda piston 6 slidably disposed in a cylinder bore 3 a in the cylinder body3 is connected to a crankshaft 8 via a connecting rod 7.

The cylinder body 3 and the crankcase 2 are securely connected togetherby screwing four case bolts 30 a which pass through a lower flangeportion (a case side flange portion) 3 b into a cylinder side matingsurface 2 e of the crankcase 2. To be more specific, the case bolts 30 aare screwed into bolt connecting portions (connecting boss portions) 12c of iron alloy bearing brackets (bearing members) 12, 12′ (which willbe described later on) embedded in left and right wall portions of thealuminum alloy crankcase 2, respectively, through insert casting. Notethat reference numeral 31 a denotes a positioning dowel pin forpositioning the crankcase 2 and the cylinder body 3.

In addition, the cylinder body 3 and the cylinder head 4 are connectedtogether with two short head bolts 30 b and four long head bolts 30 c.The short head bolt 30 b is screwed to be planted in a portion below aninduction port 4 c and a portion below an exhaust port in the cylinderhead 4, extends downwardly to pass through an upper flange portion 3 fof the cylinder block 3 and protrudes downwardly therefrom. Then, a capnut 32 a is screwed on the downwardly protruding portion of the shorthead bolt 30 b, whereby the upper flange portion 3 f and hence thecylinder body 3 are fastened to a cylinder side mating surface 4 a ofthe cylinder head 4.

In addition, the long head bolt 30 c is screwed to be planted in thelower flange portion 3 b of the cylinder body 3, extends upwardly topass from the upper flange portion 3 f of the cylinder block 3 through aflange portion 4 b of the cylinder head 4 and protrudes upwardlytherefrom. Then, a cap nut 32 b is screwed on the upwardly protrudingportion of the long head bolt 30 c, whereby the lower flange portion 3 band hence the cylinder body are fastened to the cylinder side matingsurface 4 a of the cylinder head 4.

Thus, in connecting the cylinder body 3 and the cylinder head 4together, since not only the upper flange portion 3 f of the cylinderbody 3 is fastened to be fixed to the cylinder head 4 with the shorthead bolts 30 b and the cap nuts 32 but also the long head bolts 30 care planted in the lower flange portion 3 b which is fastened to besecurely connected to the mating surface 2 e of the crankcase 2, so thatthe cylinder body 3 is fastened to be fixed to the flange portion 4 b ofthe cylinder head 4 with the long head bolts 30 c and the cap nuts 32 b,a tensile load generated by a combustion pressure comes to be borne bythe cylinder body 3 and the four long head bolts 30 c, so that a loadapplied to the cylinder body 3 can be reduced accordingly or by such anextent that the load is so borne by the cylinder body 3 and the longhead bolts 30 c. As a result, a stress generated at, in particular, anaxially intermediate portion of the cylinder body 3 can be reduced,thereby making it possible to secure a required durability even in casethe thickness of the cylinder body 3 is reduced.

Incidentally, in the event that only the upper flange portion 3 f of thecylinder body 3 is connected to the cylinder head 4, an excessivelylarge tensile stress is generated at the axially intermediate portion ofthe cylinder body 3, and in an extreme case, there occurs a concern thata crack is generated at the portion in question. In the embodiment,however, the generation of the excessively large stress at theintermediate portion of the cylinder body can be avoided due to thepresence of the long head bolts 30 c, thereby making it possible toprevent the generation of a crack.

In addition, in planting the long head bolts 30 c in the lower flangeportion 3 b, since the long head bolts are disposed in the vicinity ofthe crankcase fastening case bolts 30 a, respectively, the loadgenerated by the combustion pressure can be transmitted from thecylinder head 4 to the crankcase 2 via the long head bolts 30 c and thecylinder body in an ensured fashion, thereby making it possible toimprove the durability against the load in this respect.

Here, as shown in FIGS. 5, 16, the right-side bearing bracket 12′ has aboss portion 12 b in which a right-side bearing 11 a′ of the crankshaft8 is inserted to be fitted in a bearing hole 12 a through press fit.Then, the bolt connecting portions 12 c, 12 c extend upwardly from frontand rear portions which hold the crankshaft 8 therebetween as seen inthe direction in which the crankshaft 8 extends to the vicinity of thecylinder-side mating surface 2 e of the crankcase 2.

In addition, in the left-side bearing bracket 12, as shown in FIGS. 5,17, the bolt connecting portions 12 c, 12 c extend from front and rearportions which hold the crankshaft 8 therebetween as seen in thedirection in which the crankshaft 8 extends to the vicinity of thecylinder-side mating surface 2 e of the crankcase 2. In addition, acollar hole 12 e is formed in the boss portion 12 b into which an ironbearing collar 12 d having an outside diameter larger than that of abalancer driving gear 25 a, which will be described later on, is pressfitted. Then, a left-side crankshaft bearing 11 a is inserted to befitted in the bearing hole 12 a of the bearing collar 12 d.

Here, the bearing collar 12 d is such as to facilitate the assembly ofthe crankshaft 8 in the crankcase 2 with a gear unit 25 having thebalancer driving gear 25 a being press fitted on the crankshaft 8.

In addition, as shown in FIG. 5, a seal plate 25 d is interposed betweenthe gear unit 25 on a left shaft portion 8 c of the crankshaft 8 and thebearing 11 a. An inside diameter side portion of the seal plate 25 d isheld by the gear unit 25 and an inner race of the bearing 11 a, and aslight gap is provided between an outside diameter side portion thereofand an outer race of the bearing 11 a for avoiding the interferencetherebetween. In addition, an inner circumferential surface of a flangeportion 12 h of the bearing collar 12 d is brought into sliding contactwith an outer circumferential surface of the seal plate 25 d.

Furthermore, a seal tube 17 i is interposed between the bearing 11 a′ ofa right shaft portion 8 c′ of the crankshaft 8 and a cover plate 17 g.An inner circumferential surface of the seal tube 17 i is fixedly fittedon the right shaft portion 8 c′. In addition, a seal groove having alabyrinth construction is formed in an outer circumferential surface ofthe seal tube 17 i, and the outer circumferential surface of the sealtube 17 i is brought into sliding contact with an inner circumferentialsurface of a seal bore 2 p formed in the right case portion 2 b.

Thus, the leakage of pressure within a crank compartment 2 c isprevented by interposing the seal plate 25 d and the seal tube 17 i onthe outside of the bearings 11 a, 11 a′ on the left and right shaftportions 8 c, 8 c′ of the crankshaft 8.

Thus, according to the embodiment, since the bolt connecting portions(the connecting boss portions) 12 c, 12 c which extend toward thecylinder body 3 side are integrally formed on the sides situatedopposite across the cylinder bore axis A of each of the iron alloycrankshaft supporting bearing members 12, 12′ which are insert cast inthe aluminum alloy crankcase 2 and the case bolts 30 a for connectingthe cylinder body 3 to the crankcase 2 are screwed into the boltconnecting portions 12 c, respectively, the load generated by virtue ofthe combustion pressure can be borne uniformly by the two front and rearbolt connecting portions 12 c which are situated opposite across thecylinder bore axis A, whereby the connecting rigidity between thecylinder body 3 and the crankcase 2 can be improved.

In addition, since balance shafts 22, 22′ which are disposed in parallelwith the crankshaft 8 in the vicinity thereof are supported by the ironalloy bearing members 12, 12′ at at least one ends thereof, thesupporting rigidity of the balance shafts 22, 22′ can be increased.

Furthermore, in embedding the iron alloy bearing brackets 12, 12′ in thealuminum alloy crankcase 2, since the upper end face 12 f of the boltconnecting portion 12 c is positioned inwardly without being exposed tothe cylinder side mating surface 2 e of the crankcase 2, there is norisk that metallic members which are different in hardness and materialexist in a mixed fashion at a joint between the crankcase 2 and thecylinder block 3, thereby making it possible to avoid a reduction insealing capability. Namely, in the event that the upper end face 12 f ofthe bolt connecting portion 12 c abuts with a case side mating surfaceformed on the lower flange 3 b of the aluminum alloy cylinder body 3,the sealing capability is reduced due to a difference in thermalexpansion coefficients.

In addition, in the left-side bearing bracket 12, since the bearingcollar 12 having the outside diameter larger than that of the balancerdriving gear 25 a is attached to the outer circumference of the bearing11 a, when assembling the crankshaft 8 in the crankcase 2 with thebalancer driving gear 25 a being attached to be fixed onto thecrankshaft 8 through press fit or the like (or the balance driving gear25 a may of course be integrally formed on the crankshaft 8), there iscaused no risk that the balancer driving gear 25 a is brought intointerference with a minimum inside diameter portion of the boss portion12 b of the bearing bracket 12, and hence the assembling of thecrankshaft 8 can be implemented without any problem.

The crankcase 2 is a two-piece type in which the crankcase 2 is dividedinto the left and right case portions 2 a, 2 b. A left case cover 9 isdetachably attached to the left case portion 2 a, and a space surroundedby the left case portion 2 a and the left case cover 9 constitutes aflywheel magnet compartment 9 a. A flywheel magnetic generator 35attached to the left end portion of the crankshaft 8 is accommodated inthis flywheel magnet compartment 9 a. Note that the flywheel magnetcompartment 9 a communicates with a camshaft arranging compartment viachain compartments 3 d, 4 d, which will be described later on, wherebymost of the lubricating oil which has been used to lubricate camshaftsfalls into the flywheel magnet compartment 9 a via the chaincompartments 3 d, 4 d.

In addition, a right case cover 10 is detachably attached to the rightcase portion 2 b, and a space surrounded by the right case portion 2 band the right case cover 10 constitutes a clutch compartment 10 a.

The crank compartment 2 c and a transmission compartment 2 d are formedat front and rear portions of the crankcase 2, respectively. The crankcompartment 2 c is made to open to the cylinder bore 3 a but is definedsubstantially to be separated from the other compartments such as thetransmission compartment 2 d. Due to this, the pressure within thetransmission compartment 2 d is caused to fluctuate as the pistonreciprocates vertically, thereby allowing the transmission compartment 2d to function as a pump.

The crankshaft 8 is arranged such that left and right arm portions 8 a,8 a and left and right weight portions thereof are accommodated in thecrank compartment 2 c. The crankshaft 8 is an assembly including a leftcrankshaft portion into which the left arm portion 8 a, weight portion 8b and shaft portion 8 c are integrated and a right crankshaft portioninto which the right arm portion 8 a, weight portion 8 b and shaftportion 8 c′ are integrated, the left crankshaft portion and the rightcrankshaft portion being connected integrally via a tubular crank pin 8d.

The left and right shaft portions 8 c, 8 c′ are rotationally supportedon the side walls of the left and right case portions 2 a, 2 b via thecrankshaft bearings 11 a, 11 a′. As has been described above, thebearings 11 a, 11 a′ are press fitted in the bearing holes 12 a in theiron alloy bearing brackets 12, 12′ which are insert cast in the leftand right case portions 2 a, 2 b of aluminum alloy.

A transmission 13 is accommodated and arranged in the transmissioncompartment 2 d. The transmission 13 is such as to have a constant meshconstruction in which a main shaft 14 and a drive shaft 15 are providedand arranged in parallel with the crankshaft 8, and first-speed tofifth-speed gears 1 p to 5 p attached to the main shaft 14 are made toconstantly mesh with first-speed to fifth-speed gears 1 w to 5 wattached to the drive shaft 15.

The main shaft 14 is rotationally supported by the left and right caseportions 2 a, 2 b via main shaft bearings 11 b, 11 b, whereas the driveshaft 15 is rotationally supported by the left and right case portions 2a, 2 b via drive shaft bearings 11 c, 11 c.

A right end portion of the main shaft 14 passes through the right caseportion 2 b and protrudes to the right side, and a clutch mechanism 16is attached to the protruding portion, and this clutch mechanism 16 islocated within the clutch compartment 10 a. Then, a large reduction gear(an input gear) 16 a of the clutch mechanism 16 meshes with a smallreduction gear 17 fixedly attached to the right end portion of thecrankshaft 8.

A left end portion of the drive shaft 15 protrudes outwardly from theleft case portion 2 a and a driving sprocket 18 is attached to theprotruding portion. This driving sprocket 18 is connected to a drivensprocket on a rear wheel.

A balancer unit 19 according to the embodiment includes front and rearbalancers 20, 20′ disposed opposite across the crankshaft 8 and havingsubstantially the same construction. The front and rear balancers 20,20′ include the balance shaft 22, 22′ which do not rotate and weights24, 24 which are rotationally supported on the balance shat via bearings23, 23.

Here, the balance shafts 22, 22′ are also used as the case bolts (theconnecting bolts) for connecting the left and right case portions 2 a, 2b together in the direction in which the crankshaft extends. Therespective balance shafts 22, 22′ function to connect the left and rightcase portions together by causing flange portions 22 a formed on insidesof the rotationally supported weights 24 in a transverse direction ofthe engine to abut with boss portions 12 g of the bearing brackets 12′,12 which are insert cast into the left and right case portions 2 a, 2 band screwing fixing nuts 21 a, 21 b on opposite ends of the respectivebalance shafts.

The weight 24 includes a semi-circular weight main body 24 a and acircular gear supporting portion 24 b which is integrally formed on theweight main body, and a ring-shaped balancer driven gear 24 c is fixedlyattached to the gear supporting portion 24 b. Note that referencenumeral 24 b denotes a hole made by partially cutting away the materialof a part of the weight 24 which is situated opposite to the weight mainbody 24 a so as to reduce the weight of the part to as low a level aspossible.

The balancer driven gear 24 c attached to the rear balancer 20′ mesheswith the balancer driving gear 25 a which is rotationally attachedrelative to the gear unit 25 which is securely attached to the leftshaft portion 8 c of the crankcase 8 through press fit.

Note that reference numeral 25 b denotes a timing chain driving sprocketintegrally formed on the gear unit 15 and has, as shown in FIG. 11, analigning or timing mark 25 c for alignment of timing marks for valvetiming. The gear unit 25 is press fitted on the crankshaft 8 such thatthe timing mark 25 c aligns with the cylinder bore axis A as viewed inthe direction in which the crankshaft extends when the crankshaft 8 issituated at a top dead center of a compression stroke.

In addition, the balancer driven gear 24 c attached to the frontbalancer 20 meshes with a balancer driving gear 17 a which is supportedrotationally relative to the small reduction gear 17 which is fixedlyattached to the right shaft portion 8 c′ of the crankshaft 8.

Here, the rear balancer driving gear 25 a is supported rotationallyrelative to the gear unit 25, and the front balancer driving gear 17 ais supported rotationally relative to the small reduction gear 17. Then,U-shaped damper springs 33 each made up of a plate spring are interposedbetween the balancer driving gears 25 a, 17 a and the gear unit 25 andthe small reduction gear 17, respectively, to thereby restrain thetransmission of impact generated due to a torque fluctuation occurringin the engine to the balancers 20, 20′ is restrained from beingtransmitted.

Here, while the balancer driving gear 17 a for driving the frontbalancer 20 will be described in detail by reference to FIG. 14, thesame description would be given if the balancer driving gear 25 a fordriving the rear balancer were described. The balancer driving gear 17 ais formed into a ring shape and is supported by a sliding surface 17 bformed so as to have a smaller diameter than the small reduction gear 17rotationally relative to a side of the small reduction gear 17. Then, anumber of U-shaped spring retaining grooves 17 c are formed in thesliding surface 17 b by setting them back into the surface thereof in aradial fashion about the center of the crankshaft, and the U-shapeddamper springs 33 are arranged to be inserted in place within the springretaining grooves 17 c. Opening side end portions 33 a, 33 a of thedamper spring 33 are locked at front and rear stepped portions formed ina locking recessed portion 17 d formed in an inner circumferentialsurface of the balancer driving gear 17 a.

When a relative rotation is generated between the small reduction gear17 and the balancer driving gear 17 a due to a torque fluctuation, thedamper springs 33 resiliently deform in a direction in which the spacebetween the end portions 33 a, 33 a narrows so as to absorb the torquefluctuation so generated. Note that reference numeral 17 g denotes acover plate for retaining the damper springs 33 within the retaininggrooves 17 c, reference numeral 17 h denotes a key for connecting thesmall reduction gear 1 with the crankshaft 8, and reference numerals 17e, 17 f denote, respectively, alignment marks for use in assembling thesmall reduction gear 17 and the balancer driving gear 17 a.

A mechanism for adjusting a backlash between the balancer driven gears24 c, 24 c and the balancer driving gears 25 a, 17 a is provided on thebalancers 20, 20′. This adjusting mechanism is constructed such that thebalancer axis of the balance shaft 22, 22′ slightly deviates from therotational center of the balancer driven gear 24 c. Namely, when thebalance shaft 22, 22′ is made to rotate about the balancer axis, thespace between the rotational center line of the balancer driven gear 24c and the rotational center line of the balancer driving gear 25 a, 17 achanges slightly, whereby the backlash is changed.

Here, a mechanism for rotating the balance shaft 22, 22′ differs betweenthe front balancer 20 and the rear balancer 20′. Firstly, in the rearbalancer 20′, a hexagonal locking protruding portion 22 b is formed on aleft end portion of the rear balance shaft 22′, and a spline-like (apolygonal star-like) locking hole 26 a formed in one end of a rotationallever 26 is locked on the locking protruding portion 22 b. In addition,an arc-like bolt hole 26 b is formed in the other end portion of therotational lever 26 in such a manner as to extend about the balanceraxis.

A fixing bolt 27 a passed through the bolt hole 26 b is planted in aguide plate 28. The guide plate 28 is generally formed into an arc-likeshape and is fixedly bolted to the crankcase 2. Note that the guideplate 28 has also a function to control the flow of lubricating oil.

The adjustment of the backlash of the rear balancer 20′ is implementedby rotating the rotational lever 26 so as to bring the backlash to anappropriate state with the fixing nut 21 a being loosened and thereafter by fixing the rotational lever 26 with the fixing bolt 27 a and afixing nut 27 b, and thereafter, the fixing nut 21 a is refastened.

A grip portion 22 f having an oval cross section, which is formed byforming a flat portion 22 e on both sides of a cross-sectionallycircular shape, is formed on a left end portion of the front balanceshaft 22 (refer to FIG. 12). A collar 29 a having an innercircumferential shape which matches an outer circumferential shape ofthe grip portion 22 f is attached to the grip portion 22 f, andfurthermore, a holding portion 29 b of a holding lever 29 is attached toan outside of the collar 29 a in such a manner as to move axially but asnot to rotate relatively. A distal end portion 29 e of the holding lever29 is fixed to a boss portion 2 f of the left case portion 2 a with abolt 29 f. In addition, a tightening slit 29 c is formed in the holdingportion 29 b of the holding lever 29, so that the rotation of the collar29 and hence of the balance shaft 22 is prevented by tightening up thefixing bolt 29 d. Furthermore, the fixing nut 21 b is screwed on thebalance shaft 22 to an outer side of the collar 29 so as to be securedthereto via washer.

The adjustment of the backlash of the front balancer 20 is implementedby loosening the fixing nut 21 b or preferably removing the same,griping the grip portion 22 f of the balance shaft 22 with a tool torotate the shaft so as to bring the backlash to an appropriate state,and thereafter tightening up the fixing bolt 29 d, and thereafter, thefixing nut 21 b is fastened.

In addition, a lubricating oil introducing portion 22 c is formed in anupper portion of the locking protruding portion 22 b by cutting out theupper in an arc. A guide bore 22 d is made to open to the introducingportion 22 c, and the guide bore extends into the balance shaft 22 andpasses therethrough to below an outer circumferential surface of thebalance shaft 22, whereby the lubricating oil introducing portion 22 cis made to communicate with an inner circumferential surface of thebalancer bearing 23. Thus, lubricating oil that has fallen in thelubricating oil introducing portion 22 c is supplied to the balancerbearing 23.

Here, while the weight 24 and the balancer driven gear 24 c are disposedat the right end portion along the direction in which the crankshaftextends in the front balancer 20, in the rear balancer 20′, they aredisposed at the left end portion. In addition, the balancer driven gear24 c is located rightward relative to the weight 24 in both the frontand rear balancers 20, 20′, and therefore, the weight 24 and thebalancer driven gear 24 c are set into the same configuration in boththe front and rear balancers.

Thus, according to the embodiment, since the weight main body 24 a andthe balancer driven gear 24 c of the balancer 20 are disposed on theright-hand side (one side) of the front balance shaft (the primarybalance shaft) 22 along the direction in which the crankshaft extendsand the weight main body 24 a and the balancer driven gear 24 c aredisposed on the left-hand side (the other side) of the rear balanceshaft (the secondary balance shaft) 22′ along the direction in which thecrankshaft extends, the reduction in balance in weight in the crankshaftdirection that would result when providing a two-shaft balancer unit canbe avoided.

In addition, since the front and rear balance shafts 22, 22′ are made todouble as the case bolts for connecting the left and right case portions2 a, 2 b together, when adopting a two-shaft balancer unit, theconnecting rigidity of the crankcase can be enhanced while restrainingthe construction of the engine from becoming complex and the number ofcomponents from being increased.

Additionally, since the balancer weight main body 24 a and the balancerdriven gear 24 c are made integral and are supported rotationally by thebalance shafts 22, 22′, respectively, only the weight made up of thebalancer weight main body 24 a and the balancer driven gear 24 c may bedriven to rotate, and therefore, the engine output can be attempted tobe used effectively to such an extent that the balance shafts themselvesdo not need to be driven to rotate.

In addition, the degree of freedom in assembling can be improved whencompared with an engine construction in which a balancer weight and abalance shaft are made integral.

Additionally, since the rotational center lines of the balancer drivengears 24 c are caused to deviate relative to the axes of the balanceshafts 22, 22′, the backlash between the balancer driven gears 24 c andthe balancer driving gears 25 a, 27 a on the crankshaft 8 side can beadjusted by the simple construction or only by a simple operation ofrotating the balance shafts, thereby making it possible to prevent thegeneration of noise.

On the front balance shaft 22, the backlash adjustment is implemented bygripping the grip portion 22 f formed on the left-hand side of thebalance shaft 22 with a tool so as to rotate the balance shaft 22, andon the rear balance shaft 22′, the backlash adjustment is implemented byrotating the rotational lever 26 provided on the left-hand side of thebalance shaft 22′. Thus, on either of the front and rear balance shafts22, 22′, the backlash can be adjusted from the left-hand side of theengine, and hence the backlash adjusting work can be implementedefficiently.

Additionally, since the balancer driving gear 17 a on the crankshaft 8side which meshes with the balancer driven gear 24 c is constructed tobe disposed in such a manner as to rotate relatively to the slidingsurface 17 b of the small reduction gear 17 which is fixed to thecrankshaft 8 and the U-shaped damper springs 33 are disposed in thespring retaining grooves 17 c formed by setting them back from thesliding surface 17 b, the impact generated due to the torque fluctuationin the engine can be absorbed by the compact construction so that thebalancer unit can be operated smoothly. Note that the same descriptioncan be made with respect to the balancer drive gear 25 a.

Furthermore, a coolant pump 48 is disposed at the right end portion ofthe front balance shaft 22 coaxially therewith. A rotating shaft of thecoolant pump 48 is connected to the balance shaft 22 by an Oldham'scoupling which has a similar construction to that of a lubricating oilpump 52, which will be described later on, in such a manner that aslight deviation between the centers of the rotating shaft and thebalance shaft 22 can be absorbed.

In the valve train device of the embodiment, an intake camshaft 36 andan exhaust camshaft 37 which are disposed within the cylinder head cover5 are constructed to be driven to rotate by the crankshaft 8. To bespecific, a crankshaft sprocket a crankshaft side driving wheel) 25 b ofthe gear unit 25 press fitted on the left shaft portion 8 c of thecrankshaft 8 so as to be attached thereto and an intermediate sprocket(an intermediate driven wheel) 38 a rotationally supported by a supportshaft 39 planted in the cylinder head 4 are connected by a timing chain40, and an intermediate gear 38 formed integrally on the intermediatesprocket 38 a and having a smaller diameter than that of theintermediate sprocket 38 a meshes with intake and exhaust gears 41, 42secured to end portions of the intake and the exhaust camshafts 36, 37.Note that the timing chain 40 is disposed so as to pass through thechain compartments 3 d, 4 d formed on the left walls of the cylinderblock 3 and the cylinder head 4.

The intermediate sprocket 38 a and the intermediate gear 38 b are formedso as to be integrated into an intermediate rotational unit 38 and arerotationally supported by the support shaft 39 which passes through thechain compartment 4 d on the cylinder head 4 in the direction in whichthe crankshaft extend along the cylinder bore axis A via two sets ofneedle bearings 44. The support shaft 39 is inserted from the outside ofthe cylinder head and is fixed at a flange portion 39 a thereof to thecylinder head 4 with two bolts 39 b. Note that reference numerals 39 c,39 d denote a sealing gasket, respectively.

Here, commercially available (standard) bearings are adopted for the twosets of needle bearings 44, 44. A space adjusting collar 44 a isdisposed between the respective bearings 44, 44, and thrust washers(washer members) 44 b, 44 b for receiving thrust load to therebyrestrict the axial position of the intermediate rotational unit 38 areprovided at ends of the bearings. The thrust washer 44 b is formed intoa stepped shape having a large diameter portion which is brought intosliding contact with outer end faces of the intermediate sprocket andintermediate gear and a stepped portion 44 c which protrudes axiallytoward the needle bearing 44. The space where the bearing 44 is arrangedis regulated by the stepped portion 44 c and the collar 44 a.

Thus, since the space adjusting collar 44 a is interposed between thetwo sets of bearings 44, 44, commercially available standard bearingscan be adopted for the needle bearings by adjusting the length of thecollar 44 a and the protruding amount of the stepped portion 44 c,thereby making it possible to reduce costs. Note that in the event thatonly one needle bearing is used, the space where the bearing is arrangedis adjusted by the protruding amount of the stepped portion 44 c of thewasher member.

In addition, since the washer having the stepped configuration isadopted as the thrust washer 44 b, the assembling work of theintermediate sprocket 38 a and the intermediate gear 38 b (theintermediate rotational unit) can be improved. Namely, in assembling theintermediate rotational unit to the engine, while the support shaft 39is inserted from the outside in a state in which the intermediatesprocket 38 a and the intermediate gear 38 b are disposed within thechain compartment 4 d with the thrust washers being positioned at theends of the intermediate sprocket 38 a and the intermediate gear 38 b insuch a manner as not to fall therefrom, the thrust washer 44 b can beprevented from falling by allowing the stepped portion 44 c of thethrust washer 44 b to be locked in a shaft hole in the intermediatesprocket 38 a or the like, and hence the assembling properties can beimproved.

In addition, an oil hole 39 e is formed in the support shaft 39 forsupplying lubricating oil introduced from the cam compartment via an oilintroducing bore 4 e formed in the cylinder head 4 to the needle bearing44.

Additionally, four material cut-away weight reduction holes 38 c and twoinspection holes 38 c adapted to be used at the time of assembling andmade to double as material cut-away weight reduction holes are formed atintervals of 60 degrees. Then, an alignment or timing mark 38 d isstamped on a tooth situated substantially at the center of theinspection hole 38 c′ for the intermediate gear 38 b, and timing marks41 a, 42 a are also stamped on two teeth of intake and exhaust camshaftgears 41, 42 which correspond to the timing marks 38 d. Here, whenaligning the left and right timing marks 38 d, 38 d with the timingmarks 41 a, 42 a, the intake and exhaust camshafts gears 41, 42 arelocated at positions, respectively, which correspond to a top deadcenter of a compression stroke.

Furthermore, timing marks 38 e, 38 e are also formed at portions of theintermediate sprocket 38 a which are situated on a cover side matingsurface 4 f of the cylinder head 4 when the timing marks 38 d align with41 a, 42 a.

Here, the intermediate rotational unit 38 is disposed on a crankshaftside of the cylinder head 4 which is beyond the cover side matingsurface 4 f thereof, and the intake and exhaust camshafts 36, 37 aredisposed on an opposite side to the crankshaft side. Then, a portionwhere the camshaft gears and the intermediate gear mesh with each otheris positioned at substantially the same height of the mating surface 4f, and therefore, the outer wall of the chain compartment 4 d does notconstitute an interruption when the meshing portion is subjected tovisual inspection through the inspection holes 38′.

Here, the intake and exhaust camshafts 36, 37 are rotationally supportedby a camshaft carrier 80 in such a manner that the axes thereof arelocated at positions which are spaced away upwardly from the matingsurface 4 f of the cylinder head 4. To describe in detail, the intakeand exhaust camshafts 36, 37 are mounted on a bearing portion of acarrier main body 80 a detachably attached onto the mating surface 4 fand are held by a camshaft cap 80 b on an upper side thereof.

Note that, in FIG. 4, since a state in which the intake camshaft 36 isarranged is shown in an exploded fashion, while a bottom surface of thecarrier main body 80 a is illustrated as being spaced away from themating surface 4 a, in reality, the bottom surface of the carrier mainbody 80 a coincides with the mating surface 4 f, and this arrangementstate is shown in FIG. 3.

To align valve timings, with the left case cover 9, the generator 35 andthe cylinder head cover 5 being removed, firstly, the crankshaft 8 isheld at a top dead center of a compression stroke by aligning the timingmark 25 c (refer to FIG. 11) with the cylinder bore axis A. In addition,the intermediate sprocket 38 a and the intermediate gear 38 b which areattached to the cylinder head 4 via the support shaft 39 are positionedso that the timing mark 38 e of the intermediate sprocket 38 a alignswith the cover side mating surface 4 f, and in this state, thecrankshaft sprocket 25 b and the intermediate sprocket 38 a areconnected by the timing chain 40. Then, the intake and exhaust camshaftgears 41, 42 on the intake and exhaust camshafts 36, 37 are brought intomesh engagement with the intermediate gear 38 b while confirming throughthe inspection hole 38 c′ that the timing marks 41 a, 42 a align withthe timing mark 38 d on the intermediate gear 38 b, and the intake andexhaust camshafts 36, 37 are fixed to an upper surface of the cylinderhead 4 via the camshaft carrier 80.

Thus, since the inspection holes 38 c′ made to double as the weightreduction holes to reduce the weight of the large diameter intermediatesprocket 38 a are provided in the intermediate sprocket 38 a, so thatthe alignment of the timing marks 38 d on the small diameterintermediate gear 38 b which is set on the back of the intermediatesprocket 38 a with the timing marks 41 a, 42 a on the camshaft gears 41,42 can be confirmed through the inspection holes 38 c′, the meshingpositions of the intermediate gear 38 b with the camshaft gears 41, 42can visually confirmed in an easy and ensured fashion while the smalldiameter intermediate gear 38 b is placed on the back of the largediameter intermediate sprocket 38 a, thereby making it possible to alignthe valve timings without any problem.

In addition, since the intermediate gear 38 b can be disposed on theback side of the intermediate sprocket 38 a, the dimension from thecamshaft gears 41, 42 which mesh with the intermediate gear 38 b to acam nose 36 a can be made shorter, whereby the torsional angle of thecamshaft can be made smaller to such an extent that the dimension ismade so shorter, thereby making it possible to make compact an areasurrounding the camshafts.

Namely, for example, in a case where the intermediate gear 38 b isdisposed on a front side of the intermediate sprocket 38 a, while thevalve timings can easily be aligned, the dimension from the camshaftgears 41, 42 to the cam nose becomes long, and the torsional angle ofthe camshafts becomes large to such an extent that the dimension isextended, thereby reducing the control accuracy of valve opening andclosing timings.

In addition, in a case where the intermediate gear 38 b is disposed infront of the intermediate sprocket 38 a, a space between theintermediate sprocket support shaft 39 and the camshafts 36, 37 needs tobe expanded in order to avoid any interference between the intermediatesprocket 38 a and the camshaft 36, 37, this causing a concern that thearea surrounding the camshafts is enlarged.

Additionally, since the intermediate rotational unit 38 is arranged onthe crankshaft side of the cylinder head 4 across the mating surface 4 fof the cylinder head 4 with the cylinder head cover 5 and the camshaftgears 41, 42 are arranged on the opposite side to the crankshaft side,the meshing portion where the camshaft gears 41, 42 mesh with theintermediate gear 38 b can be positioned in the vicinity of the matingsurface 4 f, and the meshing portion can easily be visually inspectedfrom the outside.

Namely, since the camshafts 36, 37 are disposed upwardly away from themating surface 4 f, while the intermediate sprocket 38 a and theintermediate gear 38 b are positioned within the chain compartment 4 d,the meshing portion is positioned in the vicinity of the mating surface4 f, and therefore, there is caused no risk that the outer wall of thechain compartment 4 d constitutes an interruption when the meshingportion is visually inspected through the inspection holes 38 c′.

In addition, since the position alignment mark 38 e which refers to themating surface 4 f as a reference surface is formed on the outer surfaceof the intermediate sprocket 38 a, the angular positioning of theintermediate sprocket 38 a which is needed in the first place whenadjusting the valve timing can be implemented easily and securely.

Additionally, since the camshaft carrier 80 is detachably attached tothe cylinder head 4 and the camshafts 36, 37 are rotationally supportedby the camshaft carrier 80, in the event that the camshafts 36, 37 aredisposed upwardly apart from the mating surface 4 f, there can beavoided a problem that the machining properties of the cylinder headmating surface 4 f are reduced.

Namely, in the event that the camshafts are disposed upwardly apart fromthe mating surface, since the camshaft bearing portion protrudesupwardly of the mating surface 4 f, while the machining properties arereduced when compared with a case where the upper end surface of thecylinder head is flat, according to the embodiment, since theconstruction is adopted where the camshaft carrier 80 is detachablyattached, the upper end surface of the cylinder head can be made flatand the machining properties can be improved.

Additionally, since the intermediate sprocket 38 a and the intermediategear 38 b are rotationally supported by disposing the intermediatesprocket 38 a and the intermediate gear 38 b within the chaincompartment 4 d and inserting the support shaft 39 so as to be disposedin such a manner as to extend across the chain compartment 4 d, thesupporting construction can be simplified and the assembling propertiescan be improved.

Here, a backlash adjusting mechanism is provided between theintermediate gear 38 b and the camshaft gears 41, 42. This adjustingmechanism has a construction in which the intake camshaft gear 41 andthe exhaust camshaft gear 42 are made up of two gears such as a drivinggear (a power transmission gear) 46 and a shift gear (an adjusting gear)45 and the angular positions of the driving gear 46 and the shift gear45 can be adjusted.

Namely, the shift gear 45 and the driving gear 46 are fixed to flangeportions 36 b, 37 b formed at end portions of the camshafts 36, 37,respectively, in such a manner that the angular positions thereof can beadjusted by four circumferentially long elongated holes 45 a, 46 a andfour long bolts 68 a. A clearance portion 46 b is cut and formed in thedriving gear 46 that is disposed outwardly, and only the shift gear 45is fixed in such a manner that the angular position thereof can beadjusted two elongated holes 45 b and two short bolts 68 b by making useof the clearance portion 46.

A backlash adjustment is implemented according to the followingprocedure. Note that in the engine according to the embodiment, theintermediate gear 38 b rotates counterclockwise as shown in FIG. 3 whenviewed from the left-hand side of the engine. Consequently, both theintake camshaft gear 41 and the exhaust camshaft gear 42 rotateclockwise. In addition, here, while the backlash adjustment will bedescribed with respect to the intake camshaft gear 41, the samedescription would be made with respect to the exhaust camshaft gear 42.

Firstly, all the fixing bolts 68 a, 68 b of the intake camshaft gear 41are loosened, and the shift gear 45 is rotated clockwise so that frontside surfaces of teeth of the shift gear 45 in the clockwise directionslightly abut with rear side surfaces of teeth of the intermediate gear38 b in the counterclockwise direction. In this state, the shift gear 45is fixed to the flange portion 36 b of the camshaft 36 with two shortbolts 68 b. Then, the driving gear 46 is rotated counterclockwise insuch a manner that front side surfaces (driven surfaces) of teeth of thedriving gear 46 in the counterclockwise direction abut with front sidesurfaces (driving surfaces) of the intermediate gear 38 b in thecounterclockwise direction so as to obtain a required backlash, and inthis state, four long bolts 68 a are tightened up, whereby the drivinggear 46 and the shift gear 45 are fixed to the intake camshaft 36.

Thus, since the intake and exhaust camshaft gears 41, 42 are made up ofthe driving gear (power transmission gear) 46 and the shift (adjustinggear) 45 adapted to rotate relatively to the driving gear, respectively,the backlash can be adjusted by rotating the shift gear 45 relatively tothe driving gear 46 forward or backward in the rotating directions.

Note that while, in this embodiment, both the driving gear 46 and theshift gear 45 which constitute the camshaft gears 41, 42 are describedas being able to rotate relatively to the camshafts, one of the drivinggear 46 and the shift gear 45 may be adapted to rotate relatively andthe other gear may be integrated into the camshaft. In this case, it isdesirable that the gear integrated into the camshaft constitutes thepower transmission gear. Even if constructed in this way, similarfunction and advantage to those obtained by the embodiment can beobtained.

In addition, while, in the embodiment, the case has been described wherethe invention is applied to the valve train device which adopts thechain driving system, it goes without saying that the invention can alsobe applied to a valve train device which adopts a toothed belt drivingsystem, and furthermore, the invention can also be applied to a valvetrain device in which the crankshaft and the intermediate gear areconnected together via a gear train.

Next, a lubricating construction will be described. A lubrication system50 of the engine according to the embodiment is constructed such thatlubricating oil stored within a separate lubricating oil tank 51 ispicked up and pressurized by a lubricating oil pump 52 via a down tube56 c on a vehicle body frame, lubricating oil discharged from the pump52 is divided into three systems such as a cam lubricating system 53, atransmission lubricating system 54 and a crank lubricating system 55 soas to be supplied to parts needing to be lubricated at the respectivesystems, and lubricating oil used for lubricating the respective partsneeding lubrication is returned to the lubricating oil tank 51 by makinguse of pressure fluctuation occurring within the crank compartment 2 cas the piston 6 reciprocates vertically.

The lubricating oil tank 51 is formed integrally within a spacesurrounded by a head pipe 56 a, a main tube 56 b, the down tube 56 c anda reinforcement bracket 56 d of the vehicle body frame 56. Thislubricating oil tank 51 communicates with a cross pipe 56 e whichconnects lower portions of the down tube 56 c via the down tube 56 c.

Then, the cross pipe 56 e communicates with a pick-up port of thelubricating oil pump 52 via an outlet tube 56 f connected thereto, anoil hose 57 a, a joint pipe 57 b and a pick-up passageway 58 a formed ina crankcase cover 10. A discharge port of the lubricating oil pump 52 isconnected to an oil filter 59 via an oil discharge passageway 58 b, anexternal portion connecting chamber 58 c and an oil passageway 58 d andis divided into the three lubrication systems 53, 54, 55 on a secondaryside of the oil filter 59.

The oil filter 59 is constructed such that an oil element 59 e isdisposed in a filter compartment 59 d defined by detachably attaching aportion of a cover 47 to a filter recessed portion 10 b provided in theright case cover 10 by setting part thereof further back from the rest.

The cam lubricating system 53 has a construction which is generallyconstructed such that a lower end of a vertical member 53 a of aT-shaped lubricating oil pipe is connected to a cam side outlet 59 a ofan oil passageway formed on the outside of the filter recessed portion10 b, whereas left and right ends of a horizontal member 53 b of thelubricating oil pipe are connected to a camshaft oil supply passageway53 c, so that lubricating oil is supplied to parts such as bearings ofthe camshafts 36, 37 which need to be lubricated via the passageway 53c.

The transmission lubrication system 54 has the following construction. Aright transmission oil supply passageway 54 a formed within the rightcase portion 2 b is connected to a transmission side outlet 59 b of theoil filter 59, and the oil supply passageway 54 a communicates with theinterior of a main shaft bore 14 a formed in the mainshaft 14 along theaxial center thereof via a left transmission oil passageway 54 b formedin the left case portion 2 a. Then, this main shaft bore 14 acommunicates with sliding portions between the main shaft 14 andchange-speed gears via a plurality of branch bores 14 b, wherebylubricating oil supplied to the main shaft bore 14 a passes through thebranch bores 14 b to be supplied to the sliding portions.

In addition, an intermediate portion of the left transmission oilpassageway 54 b communicates with a bolt bore 60 a through which a casebolt 60 for connecting the left and right case portions 2 a, 2 btogether is allowed to pass. This bolt bore 60 a is such as to be formedby forming a bore having an inside diameter which is slightly largerthan the outside diameter of the case bolt 60 in tubular boss portions60 c, 60 c which are formed so as to face and abut with each other onthe mating surface between the left and right case portions 2 a, 2 b.The boss portion 60 c is situated in the vicinity of a portion where agear train on the main shaft 14 meshes with a gear train on the driveshaft 15, and a plurality of branch bores 60 b are formed from whichlubricating oil within the bolt bore 60 a is spouted out toward the geartrains meshing portion. Note that the bolts 60 shown in FIG. 19 as beingdeveloped into the left and right case portions are the same bolt.

Furthermore, a right end portion of the bolt bore 60 a communicates witha drive shaft bore 15 a formed in the drive shaft 15 along the axialcenter thereof via a communication bore 54 c. Then, the drive shaft bore15 a is closed by a partition wall 15 c at a left-hand side portion andcommunicates with sliding portions between the drive shaft 15 anddriving gears via a plurality of branch bores 15 b. Thus, lubricatingoil supplied into the drive shaft bore 15 a passes through the branchbores 15 b to be supplied to the sliding portions.

The crank lubricating system 55 has the following construction. A crankoil supply passageway 55 a is formed in the filter cover 47 in such amanner as to extend from a crank side outlet 59 c toward the lubricatingoil pump 52, and the passageway 55 is made to communicate with acommunication bore 62 a which is formed in a rotating shaft 62 of thelubricating oil pump 52 to pass therethrough along the axial centerthereof. Furthermore, the communication bore 62 a communicates with acrank oil supply bore 8 e formed in the crankshaft 8 to passtherethrough along the axial center thereof via a connecting pie 64.Then, this crank oil supply bore 8 e communicates with the interior of apin bore 65 a in a crank pin 65 via a branch bore 8 f, and the pin bore65 a is made to open to the rotating surface of a needle bearing 7 b ata big end portion 7 a of a connecting rod 7 via a branch bore 65 b.Thus, lubricating oil filtered in the oil filter 59 is supplied to therotating surface of the needle bearing 7 b.

The lubricating oil pump 52 has the following construction. A pumpcompartment 61 c is provided in a right case 61 b of a two-piece casingmade up of left and right cases 61 a, 61 b by setting a relevant portionof the case further back from the rest, and a rotor 63 is disposedrotationally within the pump compartment 61. The rotating shaft 62 isinserted into the rotor 63 along the axial center thereof in such amanner as to pass therethrough to be disposed in place therein, and therotating shaft 62 and the rotor 63 are fixed together with a pin 63 a.Note that the oil pick-up passageway 58 a and oil discharge passageway58 b are connected to a pump compartment upstream side and a pumpcompartment downstream side of the left case 61 a, respectively. Inaddition, reference numeral 66 denotes a relief valve for retaining thedischarge pressure of the lubricating oil pump 52 to a predeterminedvalue of lower and adapted to relieve the pressure on the discharge sideof the lubricating oil pump 52 to the oil pick-up passageway 58 a sidewhen the pressure on the discharge side reaches or exceeds thepredetermined value.

The rotating shaft 62 is a tubular shaft which passes through the pumpcase 61 in the axial direction and opens to the crank oil supplypassageway 55 a at a right end portion thereof as shown in the drawing.In addition, a power transmitting flange portion 62 b is formedintegrally at a left end portion of the rotating shaft 62 as shown inthe drawing. The flange portion 62 b faces a right end face of thecrankshaft 8, and the flange portion 62 b and the crankshaft 8 areconnected together by an Oldham's coupling 67 in such a manner as toabsorb a slight deviation of the centers of the shafts.

The Oldham's coupling 67 is constructed such that a coupling plate 67 ais disposed between the crankshaft 8 and the flange portion 62 b, a pin67 b planted in the end face of the crankshaft 8 and a pin 67 c plantedin the flange portion 62 b are inserted into a connecting bore 67 d inthe coupling plate 67 a.

In addition, the connecting pipe 64 is such as to connect a right endopening in the crankshaft 8 to a left end opening in the rotating shaft62, and sealing is provided by an oil seal 64 a between the innercircumference of the crankshaft opening and the inner circumference ofthe rotating shaft opening and the outer circumference of the connectingpipe 64.

Here, as has been described above, the crank compartment 2 c is definedseparately from the other transmission compartment 2 d, the flywheelmagnet compartment 9 a and the clutch compartment 10 a, whereby an oilreturn mechanism is constructed in which the pressure within the crankcompartment 2 c is fluctuated to be positive and negative as the piston6 strokes, so that lubricating oil in the respective compartments isreturned to the lubricating oil tank 51 by virtue of the pressurefluctuation.

To describe this in detail, a discharge port 2 g and a suction orpick-up port 2 h are formed in the crank compartment 2 c. A dischargeport reed valve 69 adapted to open when the pressure within the crankcompartment is positive is disposed in the discharge port 2 g, and apick-up port reed valve 70 adapted to open when the pressure within thecrank compartment is negative is disposed in the pick-up port 2 h.

Then, the discharge port 2 g communicates with the clutch compartment 10a from the crank compartment 2 c via a communication bore 2 i and thencommunicates with the transmission compartment 2 d from the clutchcompartment 10 a via a communication bore 2 j. Furthermore, thetransmission compartment 2 d communicates with the flywheel magnetcompartment 9 a via a communication bore 2 k. A return port 2 m formedso as to communicate with the flywheel magnet compartment 9 acommunicates with the lubricating oil tank 51 via a return hose 57 c, anoil strainer 57 d and a return hose 57 e.

Here, a guide plate 2 n is provided at the return port 2 m. This guideplate 2 n has a function to ensure the discharge of lubricating oil bymodifying the return port 2 m so as to provide a narrow gap a between abottom plate 2 p and itself and to secure a wide width b.

Additionally, an oil separating mechanism for separating oil mistscontained in the air within the tank by virtue of centrifugal force soas to return oil mists so separated to the crank compartment 2 c. Thisoil separating mechanism has a construction in which an introductionhose 72 a which is connected to an upper portion of the lubricating oiltank 51 at one end thereof is tangentially connected to an upper portionof a cone-shaped separating compartment 71 at the other end and a returnhose 72 b connected to a bottom portion of the separating compartment 71is connected to the pick-up port 2 h of the crank compartment 2 c. Notethat the air from which the oil mists are separated is discharged to theatmosphere via an exhaust hole 72 c.

Thus, according to the embodiment, since the crank chamber 2 c is madeto be a substantially closed space so that the pressure thereinfluctuates as the piston 6 reciprocates vertically, whereby lubricatingoil that has flowed into the crank compartment 2 c is sent back to thelubricating oil tank 51 by virtue of pressure fluctuation within thecrank compartment 2 c, the necessity of an exclusive oil sending pump (ascavenging pump) can be obviated, and hence the construction of theengine can be simplified and costs can be attempted to be reduced.

In addition, since the discharge port reed valve (an outlet side checkvalve) 69 adapted to open when the pressure in the crank compartmentincreases and to close when the pressure lowers is disposed in thevicinity of where the oil sending passageway is connected to the crankcompartment 2 c, the lubricating oil within the crank compartment 2 ccan be sent back to the lubricating oil storage tank 51 in a moreensured fashion.

In addition, since an portion above the oil level within the lubricatingoil storage tank 51 is connected to the crank compartment 2 via thereturn hoses 72 a, 72 b and the discharge port reed valve (a pick-upside check valve) 70 adapted to open when the pressure in the crankcompartment 2 c lowers and to close when the pressure increases isprovided in the vicinity where the return hoses are connected to thecrank compartment 2 c, air required is picked up into the crankcompartment 2 c when the piston 6 moves upwardly, whereas the insidepressure of the crank compartment 2 c increases as the piston 6 lowers,whereby lubricating oil within the crank compartment 2 c can be senttout in a more ensured fashion.

Incidentally, in a case where there is provided no air supply path fromthe outside to the interior of the crank compartment 2 c, only anegative pressure or a lower positive pressure is formed inside thecrank compartment, this causing a concern that there occurs a case whereoil cannot be sent out properly.

Furthermore, since the centrifugal lubricating oil mist separatingmechanism 71 for separating lubricating oil mist is interposed at theintermediate position along the length of the return passageways 72 a,72 b, so that lubricating oil mist so separated is returned to the crankcompartment 2 c via the return hose 72 b, whereas air from which themist content is removed is discharged to the atmosphere, onlylubricating oil mist can be returned to the crank compartment, wherebythe reduction in oil sending efficiency can be avoided which would occurwhen an excessive amount of air is allowed to flow into the crankcompartment, thereby making it possible to send out lubricating oil inthe crank compartment in an ensured fashion while preventing theatmospheric pollution.

In addition, since the lubricating oil pump 52 is disposed so as to beconnected to the one end of the crankshaft 8 and the discharge port ofthe lubricating oil pump 52 is made to communicate with the crank oilsupply bore (an in-crankshaft oil supply passageway) 8 e formed withinthe crankshaft 8 via the communication bore (an in-pump oil supplypassageway) 62 a formed within the lubricating oil pump 52 and theconnecting pipe 64, the lubricating oil can be supplied to the parts ofthe crankshaft 8 which need to be lubricated by the simple and compactconstruction.

In addition, since the crankshaft 8 and the lubricating oil pump 52 areconnected together by the Oldham's coupling 67 which can absorb thedisplacement of the shafts in the direction normal thereto and thecommunication bore 62 a and the crank oil supply bore 8 e are made tocommunicate with each other via the connecting pipe 64 with the O rings64 a having elasticity being interposed between the connecting pipe 64and the communicating bore 62 a, the crank oil supply bore 8 e, even inthe event that the centers of the crankshaft 8 and the pump shaft 62 arecaused to deviate slightly from each other, lubricating oil can besupplied to the parts needing to be lubricated without any problem,thereby making it possible to secure the required lubricatingproperties.

Furthermore, since the tubular boss portion 60 c is formed in thevicinity of the main shaft 14 and the drive shaft 15 which constitutethe transmission, the crankcase connecting case bolt 60 is inserted intothe bolt bore 60 a in the boss portion 60 c so that the space betweenthe inner circumferential surface of the bolt bore 60 a and the outercircumferential surface of the case bolt 60 is made to form thelubricating oil passageway, and the branch bore (the lubricating oilsupply bore) 60 b is formed which is directed to the change-speed gearsat the boss portion 60 c, lubricating oil can be supplied to the meshingsurfaces of the change-speed gears while obviating the necessity ofproviding an exclusive lubricating oil supply passageway.

In addition, since the other end of the lubricating oil passagewaydefined by the inner circumferential surface of the bolt bore 60 c andthe outer circumferential surface of the case bolt 60 is made tocommunicate with an opening of the drive shaft bore (the lubricating oilpassageway) 15 a formed within the drive shaft 15 which is situatedopposite to an outlet side of the bore, lubricating oil can be suppliedto the portions on the drive shaft 15 which are brought into slidingcontact with the change-speed gears while obviating the necessity ofproviding an exclusive lubricating oil supply passageway.

Note that while the embodiment has been described as the invention beingapplied to a so-called DOHC engine which is provided with the intakecamshaft and the exhaust camshaft, the invention can, of course, beapplied to a so-called SOHC which is provided with a single camshaftwhich is made to function as both an intake camshaft and an exhaustcamshaft as required.

Industrial Applicability

According to the first aspect of the invention, since the intermediategear is made smaller in diameter than the intermediate driven wheel andis disposed behind the intermediate driven wheel and furthermore theinspection hole is formed in the intermediate driven wheel forvisualizing the meshing portion where the intermediate gear and thecamshaft gear mesh with each other, the meshing position between theintermediate gear and the camshaft gear can be visually observed easilyand securely while the small-diameter intermediate gear is disposedbehind the large-diameter intermediate driven wheel, thereby making itpossible to carry out valve timing without any problem.

In addition, since the intermediate gear can be disposed behind theintermediate driven wheel, the dimension from the camshaft gear whichmeshes with the intermediate gear to the cam nose can be made shorter,and therefore, the torsional angle of the camshaft can be reducedaccordingly, thereby making it possible to improve the valve opening andclosing timing control accuracy. In addition, the area surrounding thecamshaft can be made compact.

According to the second aspect of the invention, since the intermediatedriven wheel and the intermediate gear are disposed on the crankshaftside across the mating surface of the cylinder head with the cylinderhead cover, whereas the camshaft gear is disposed on the opposite sideto the crankshaft side across the mating surface, the meshing portionwhere the intermediate gear meshes with the camshaft gear is positionedin the vicinity of the mating surface, there by making it possible tofacilitate the visual observation of the meshing portion from theoutside.

According to the third aspect of the invention, since the positionalignment mark which refers to the mating surface as a reference surfaceis formed on the outer surface of the intermediate driven wheel, thealignment of the angular position of the intermediate driven wheel whichis required in the first place in adjusting valve timing can beimplemented easily and securely.

According to the fourth aspect of the invention, since the camshaftcarrier is detachably attached to the cylinder head and the camshaft isrotationally mounted on the camshaft carrier by means of the camshaftcap, there can be eliminated a problem of the machining properties ofthe cylinder head mating surface being reduced which would result whenthe camshaft is disposed on the opposite side to the crankshaft sideacross the mating surface in such a manner as to be apart from themating surface.

According to the fifth aspect of the invention, since the intermediaterotational unit into which the intermediate sprocket which is theintermediate driven wheel and the intermediate gear are integrated isdisposed within the chain compartment formed on the side wall of thecylinder head and is rotationally supported by the support shaft whichis inserted to be disposed across the chain compartment, the supportingconstruction of the intermediate rotational unit can be simplified andthe assembling properties can be improved.

According to the sixth aspect of the invention, since the washer memberis disposed between the intermediate rotational unit and the wallsurface of the chain compartment for regulating the axial position ofthe intermediate rotational unit and the axial arrangement space for thebearing, commercially available bearings can be adopted without anymachining, thereby making it possible to reduce costs.

According to the seventh aspect of the invention, since the camshaftgear is made up of the power transmission gear and the adjustment gearwhich is made to rotate relative to the power transmission gear, wherebythe backlash is adjusted by causing the adjustment gear to relativelyrotate forward in the rotating direction relative to the powertransmission gear so that the tooth faces of the intermediate gear areheld between the tooth faces of the adjustment gear and the tooth facesof the power transmission gear.

1. An engine valve train device in which an intermediate driven wheeldisposed in the vicinity of a camshaft is driven by a crankshaft-sidedriving wheel formed on a crankshaft and a camshaft gear fixed to thecamshaft is driven by an intermediate gear disposed on a support shafton which the intermediate driven wheel is disposed, the intermediategear integrally rotating with the intermediate driven wheel, the enginevalve train device being characterized in that a reduction ratio fromthe crankshaft-side driving wheel to the intermediate driven wheel isset larger than a reduction ratio from the intermediate gear to thecamshaft gear, in that the intermediate gear is made smaller in diameterthan the intermediate driven wheel to such an extent that a pitch circleof the intermediate gear passes substantially an intermediate between adiameter of a boss and a pitch circle of the intermediate driven wheeland the intermediate gear is disposed on a back side of the intermediatedriven wheel, in that an inspection hole is formed in the intermediatedriven wheel for visualizing a meshing portion where the intermediategear and the camshaft gear mesh with each other, and in that analignment mark is formed on a tooth portion of the intermediate gear andthe camshaft gear, respectively.
 2. An engine valve train device as setforth in claim 1, characterized in that the intermediate driven wheeland the intermediate gear are disposed on a crankshaft side across amating surface of a cylinder head with a cylinder head cover, whereasthe camshaft gear is disposed on an opposite side to the crankshaft sideacross the mating surface, and in that the meshing portion where theintermediate gear meshes with the camshaft gear is positioned in thevicinity of the mating surface.
 3. An engine valve train device as setforth in claim 1 or 2, characterized in that a position alignment markwhich refers to the mating surface as a reference surface is formed onan outer surface of the intermediate driven wheel.
 4. An engine valvetrain device as set forth in claim 3, characterized in that a camshaftcarrier is detachably attached to the cylinder head, and in that thecamshaft is rotationally mounted on the camshaft carrier by means of acamshaft cap.
 5. An engine valve train device as set forth in claim 4,characterized in that the intermediate driven wheel is an intermediatesprocket around which a timing chain is wound and is formed integrallywith the intermediate gear to constitute an intermediate rotationalunit, and in that the intermediate rotational unit is disposed within achain compartment formed on a side wall of the cylinder head in such amanner that a rotational shaft of the intermediate rotational unit islocated closer to the crankshaft side than the mating surface and isrotationally supported via a bearing by a support shaft which isinserted to be disposed in such a manner as to extend across the chaincompartment.
 6. An engine valve train device as set forth in claim 5,characterized in that a washer member is disposed between theintermediate rotational unit and a wall surface of the chain compartmentfor regulating an axial position of the intermediate rotational unit andan axial arrangement space for the bearing.
 7. An engine valve traindevice as set forth in claim 6, characterized in that the camshaft gearcomprises a power transmission gear for transmitting a driving forcefrom the intermediate gear to the camshaft and an adjustment gear foradjusting a backlash between the power transmission gear and theintermediate gear, the adjustment gear being made to rotate relative tothe power transmission gear, whereby the backlash is adjusted by causingthe adjustment gear to relatively rotate forward in a rotating directionrelative to the power transmission gear.
 8. An engine valve train deviceas set forth in claim 1, characterized in that an alignment mark isformed on each tooth portion of an intake camshaft gear and an exhaustcamshaft gear disposed on the intake camshaft and the exhaust camshaftrespectively and on a tooth portion of the intermediate gear, in thatthe intermediate driven wheel is formed with an inspection hole forvisualizing the alignment marks of the intake camshaft gear and theintermediate gear and an inspection hole for visualizing alignment marksof the exhaust camshaft gear and the intermediate gear, and in that thealignment marks of the intake camshaft gear and the intermediate gearand the alignment marks of the exhaust camshaft gear and theintermediate gear are visible at the same time.